For the pumping of waste water centrifugal pumps are generally used, which can be started only if there is liquid in the pump body. The present invention is for an evacuation system to ensure that there is liquid in the pump body during start up and operation.
The supply of waste water to the pump is often irregular and occasionally nil. If nothing is done, the liquid level of the system will then fall so that air penetrates the pump body at a small or large extent. Also during operation air may occur in the pump body due to a too small supply of liquid or for other reasons. The pumping may then be interrupted, in spite of that, there is a small inflow of waste water. The waste water may also contain various kinds of contaminations, which cause difficulties and plugging, especially in connection with interruptions of the process.
In order to restart pumps which have been emptied of liquid it is known in the art to make use of evacuation systems, which create a vacuum at the low side of the pumps, so that liquid is lifted to the pumps. Such an evacuation system includes a closed container with a level sensor, i. e. a floater, and is mounted to the inlet tube of the pump. At the outlet side there is mounted a valve which is controlled by signals from the floater. After an interruption a vacuum pump evacuates the air from the pump through the container until it is filled with so much liquid that the floater raises and gives a starting signal to the pump. The system also controls and opens the outlet valve. If the level in the container of the floater falls, the vacuum unit will start again and evacuate the air until there is another signal from the floater.